This invention relates to the art of blow molding articles of organic plastic material from a parison and has for its principal object the provision of improved, oriented hollow articles and a method and apparatus for obtaining same.
The art teaches various methods and apparatus for obtaining blow molded articles of organic plastic material from a parison, such as in U.S. Pat. No. 3,349,155 and Re. No. 27,104. Generally, these methods are chracterized by forming a parison in a parison mold on a blow core, placing said formed parison and blow core into a blow mold and expanding said parison in the blow mold by means of fluid pressure.
Naturally, the blowing procedure inherently produces orientation in the plastic due to expansion in a radial direction; however, it is highly desirable to produce orientation in the axial direction as well. Heretofore, this has been done by reheating the parison and, before blowing, axially orienting the parison, such as by stretching.
Such known methods are subject to disadvantageous aspects. A particular disadvantage has been the difficulty of maintaining uniform wall thickness. Obviously, control of wall thickness distribution is quite important. Other difficulties include insufficient control of the parison dimensions and degree of orientation and time consuming and inconvenient operations.